We're going to hear next about the Second Amendment to the U.S. Constitution. It's a short one.

MICHAEL WALDMAN: One sentence, lots of commas and lots of confusion.

MONTAGNE: Michael Waldman has written an entire book on that amendment. He's the president of the Brennan Center for Justice at NYU's School of Law. It's called "The Second Amendment: A Biography." He spoke with Steve Inskeep.

STEVE INSKEEP, HOST:

Waldman contends the interpretation of the amendment's single sentence has repeatedly changed over time. Let's begin the discussion with the words themselves.

WALDMAN: A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed.

INSKEEP: One recent Supreme Court interpretation of those words came in 2008. Justice Antonin Scalia found the Second Amendment guaranteed an individual right to own a gun. Michael Waldman says past Supreme Court justices interpreted the same words differently.

There have always been guns, he says, and there have always been gun laws. The question always is where to draw the line, which changes from generation to generation. When the founding fathers wrote the amendment, some feared an overpowering central government, so they wanted state-armed forces, militias that could defend against that.

WALDMAN: James Madison, in the Federalist papers, said, well, we don't have to worry about a dictatorial U.S. government or a tyrannical U.S. Army because the states have their militias, and we could win a civil war if we had to. It was a different way of looking at it. People ask me all the time, so did the Second Amendment protect militias or an individual right to a gun? I think the answer is both and neither. It protected the individual right to a gun to fulfill the duty to serve in the militia. So, you know, to the framers, our question makes no sense, just as to us, their answer makes no sense.

INSKEEP: OK, so you're saying that it's a law from a different time, addressing circumstances that may no longer apply. But does that mean that the law is irrelevant? It's still part of the Constitution.

WALDMAN: No, well, that's right. Our view of the Second Amendment has evolved, and it's always been the subject of fighting, of political debate - not by consulting some pristine, constitutional text by what we think right now at any moment the Constitution means.

INSKEEP: OK, so take me through some of those changes over the last couple hundred years.

WALDMAN: Well, one period came after the Civil War. You had effectively a race war in the South. The newly freed slaves were terrorized by the Ku Klux Klan. And the people who wrote the 14th Amendment wanted to make sure that the newly freed slaves could get access to guns.

INSKEEP: Let's remind people that the 14th Amendment says you cannot discriminate on the basis of race, if I'm not mistaken.

WALDMAN: And the people who wrote that, many of them, one of the things they meant was you have to have equal rights to get a gun because otherwise the Ku Klux Klan was coming in and slaughtering former slaves and terrorizing them.

INSKEEP: So now people were thinking about the Second Amendment as individual self-defense as opposed to being part of some collective militia system.

WALDMAN: That's right. Just as the time of the founders was very different, the time of the immediate post-Civil War, which was guerrilla warfare in the South, was also very different. Then you had a period of time, the country grew West. There were more people with guns, and even then, there were gun laws, too. There's a wonderful photo from Dodge City, the archetypal frontier town.

INSKEEP: Right.

WALDMAN: It's a dusty street, and in the middle of the street is a sign that says, welcome to Dodge City, firearms strictly prohibited. So even then, there was more nuanced sense of what the right to keep and bear arms meant than sometimes we might imagine.

INSKEEP: In other words, this was never seen as an absolute right, so far as you know.

WALDMAN: The right to keep and bear arms from the beginning was something that was not an absolute right. It was based on public need and public safety as well as individual freedom. The very first federal gun law came in the 1930s, and for that, you can thank John Dillinger - the bank robbers because they had new technology in the form of sawed-off shotguns and guns from World War I and a getaway car, which was a very brand-new dangerous technology. So they passed federal gun laws.

So I think we now have to decide as a country how we want to balance individual rights and public safety. It's not really going to be up to the framers. It's really up to us. And again, that is how we've always made constitutional change. It's really always been a matter of moving public opinion before the courts will ever move.

INSKEEP: Is that in some ways a creepy way to think about the Constitution, though? Because it suggests that a public opinion poll can change the law without the law actually changing.

WALDMAN: You know, I'm a big fan of something Abraham Lincoln said. He said, with public sentiment, everything is possible. Without public sentiment, nothing is possible. Molding public sentiment, in some ways, is more powerful than being a judge or legislator because you create the context for what judges and legislators can do.

When you actually look at the rambunctious, robust history of our country, what we thought the Second Amendment meant had everything to do with what we thought of government - whether we were comfortable with a strong central government, whether we wanted more libertarian approach, as in many cases in recent years. One of the big turning points in this came in the 1970s when you had the backlash against the liberalism of the 1960s. And the National Rifle Association, at that point, it primarily represented hunters. And much more conservative, much more gun-rights oriented group won control of the organization and turned the NRA from being a group that spoke mostly for hunters, to a group that spoke mostly for the Second Amendment.

INSKEEP: Is there a way in which modern-day conservatives actually have captured some of the original spirit of this amendment? Because there was concern about a king, there was concern about tyranny, and if you listen to conservative lines of argument they're worried about an overpowering central government.

WALDMAN: Well, you know, yes, you're right in the following sense that the original worry that prompted the Second Amendment was the fear of a king with the fear of a central army. What it was protecting was a state government, local institution - the militia. So it's not wrong that these notions of individual freedom and concern about central power have animated this debate over time and animated a lot of these concerns now. Again, though, you had guns and people carrying guns and owning guns, and you had gun laws. In other words, it's never been interpreted really as giving an unfettered absolute right to do whatever you want with your gun.

INSKEEP: Michael Waldman is the author of the "Second Amendment: A Biography." Thanks very much.

WALDMAN: My pleasure.

MONTAGNE: And this is MORNING EDITION from NPR News. I'm Renee Montagne.